The present invention relates to the earth boring art and more particularly to a rotary drill bit with structure for preventing liquid in the borehole from contacting and damaging the bearings of the bit. The bit of this invention is generally used to drill mining and blast holes and the like by the rotary drilling method. In the drilling of such earth bores, air or other gaseous fluid is used as the medium for cooling the bit and for carrying cuttings from the bottom of the hole or well bore to the surface. The fluid is displaced downwardly through the interior of a rotary drill string to the drill bit. The fluid passes through the drill bit and then upwardly through the annular space between the drill string and the wall of the well bore carrying with it the drill cuttings.
In the blast hole drilling industry there has long been a need for backflow shutoff valving inside the bit which will prevent water and cuttings from flowing into the bit body and clogging the nozzles and bearing air passageways whenever there is a loss of circulating air flow. When a water producing zone or formation has been encountered, stopping the air circulation permits water to rise in the well bore. As the water rises, it can flow upwardly through the drill bit and into the interior of the drill string. Loose cuttings formed during the drilling operation are frequently carried with the water into the drill string and bit. When drilling is resumed the air circulation will be restarted. The cuttings contained in the water may plug the cooling passageways in the bit and restrict air flow. Under such circumstances air is prevented from reaching the bit bearings, resulting in overheating and softening of the bearings thereby destroying the usefulness of the bit. When this occurs, it is necessary to remove the drill string from the well and replace the bit. Such a procedure is time consuming and very expensive.
Due to the extreme weights exerted on the drill bits, considerable heat is generated in the bearings. It is therefore essential that a constant and substantial flow of air be maintained through the bearings to prevent overheating and its attendant problems. Generally, air drilling bits are constructed with one of two types of flow passageways. In one, which is generally referred to as a regular bit, the main stream of air utilized to carry the cuttings from the bottom of the well bore passes through a central opening extending through the drill bit. A plurality of cooling passageways extend from the central opening to a point adjacent the bearings of the bit for the purposes of cooling the bearings. In the other, which is referred to as a jet type bit, the air stream for carrying cuttings from the bottom of the well bore enters a central recess in the bit and exits therefrom through three jet passageways. The air passes through orifices located in the jet passageways forming relatively high velocity streams directed to engage the bottom of the well bore between the cutting members of the bit. A plurality of cooling passageways extend from the central recess to a point adjacent the bearings of the bit for the purpose of cooling the bearings. The present invention may be employed with either the regular bit or the jet bit.